Corrosion Fatigue Crack Propagation Behavior of 2219 Aluminum
Date
1989-09
Authors
Kishchuk, Thomas Peter
Journal Title
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Publisher
ORCID
Type
Degree Level
Masters
Abstract
The safety and operating life of engineering structures can, to a large extent, depend on the environmentally enhanced fatigue crack propagation behavior of the component material. A common mode of failure is corrosion fatigue, the progressive cracking of a material due to the combined action of a repeated cyclic stress and an aggressive environment. Aircraft are a prime example of where corrosion fatigue performance is a major consideration in the reliability and integrity of the structure.
This thesis examines the corrosion fatigue crack propagation behavior of 2219 aluminum. The effect of environment, loading frequency, temperature and heat treatment on crack growth rate in 2219 aluminum was investigated using ASTM standard test procedures. The effect of environment on crack growth was determined using air at 25°C and 3.5 percent sodium chloride (NaCl) solution at 25°C. The effect of loading frequency was investigated for frequencies ranging from 0.5 to 5 Hz in air at 25°C and in 3.5 percent NaCl solution at 25 and 70°C. The effect of temperature was determined in 3.5 percent NaCl solution at 25 and 70°C. Aluminum alloy 2219 in the T851 and T6 condition was used to investigate the effect of heat treatment on crack growth.
A test apparatus was developed to conduct fatigue crack propagation studies of compact tension specimens immersed in aqueous environments at elevated temperatures. Fatigue crack growth data was obtained using a microcomputer based data acquisition system. Automation of fatigue crack growth data acquisition facilitated the long term testing required to determine fatigue crack growth behavior at frequencies below 5 Hz.
Tests results indicate that 2219-T851 and 2219-T6 aluminum generally have good resistance to environmentally enhanced fatigue crack propagation in 3.5 percent NaCl solution at ambient temperatures. The largest influence of the environment was observed in 2219-T6 aluminum tested at 0.1 Hz in 3.5 percent NaCl; crack growth rates were 2.5 to 3 times greater at a given AK level than crack growth rates observed in air. Relatively slow crack growth or crack arrest was observed in 2219-T851 and 2219-T6 aluminum tested at 0.1 and 0.5 Hz in 3.5 percent NaCl at 70°C. Examination of crack paths in specimens tested under these conditions revealed crack blunting or transgranular crack branching. Further investigation is required to better understand material behavior under these conditions.
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Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering